Constellation Energy Partners LLC, Baltimore, (NYSE: CEP) plans to acquire Amvest Osage Inc., a subsidiary of privately held, Charlottesville, Va.-based Amvest Corp., for $240 million. Amvest Osage owns producing and undeveloped properties in the Cherokee Basin in Oklahoma, including a 560,000-net-acre concession for coalbed-methane and shale rights from the Osage Native American Nation. The assets feature 370 producing wells with a general 100% working interest. Amvest Osage will become a subsidiary of Constellation. Net production is approximately 16 million cubic feet of gas equivalent per day. Proved reserves as of March 31 were 93 billion billion cubic feet equivalent.